This invention relates to a photosensitive composition suited as a resist used in a fine working of a semiconductor device (particularly large scale integrated circuit (LSI)), a thin-film magnetic head such as hard disc drive and a liquid crystal display, and a method for forming a pattern and a method for manufacturing electronic parts.
In the field of electronic parts to which various kinds of fine workings are required, including a semiconductor integrated circuit device such as LSI, a thin-film magnetic head such as hard disc drive, and a liquid crystal display, a fine pattern is formed by means of a photolithography technique using a resist. Particularly, the formation of a more fine resist pattern has recently been required with the diversification as well as realization of a wide variety of functions and high density. As one measure for forming a fine resist pattern, for example, there is a realization of short wavelength of a light source for light exposure. Recently, a technique for forming a resist pattern using, as a light source for light exposure, short-wavelength light such as ArF excimer laser (193 nm) and quintuple harmonic (213 nm) of YAG laser has been developed.
However, since a normal resist material transmits light in this wave-length in an order of only about 1/30+L micron so that exposure light cannot sufficiently reach the part far from the surface of a resist film at the exposure, i.e. the substrate side portion of the resist film. As a result, such a resist material has a problem that it is difficult to form a fine pattern even if exposure light source with a short wavelength is used.
In order to sufficiently exert an effect for realize such short wavelength of the exposure light thereby forming a fine pattern, a resist having high transparency to light with the above wavelength is essential. Furthermore, in order to perform a fine working of a wiring pattern by making using of the resulting resist pattern as an etch mask, it is required for the resist to have sufficient dry etch resistance.
Therefore, Jnp. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-)4-39665 discloses, as a resist material having excellent light transparency, a resist comprising copolymer obtained by copolymerizing a monomer having an aliphatic hydrocarbon in its skeleton and a monomer having an alkali-solubility. This resist has excellent light transparency and sufficient dry etch resistance, but is inferior in solubility to a developer. The copolymer to be contained in this resist is a polymer obtained by copolymerizing two kinds of monomers having physical properties which conflict each other, i.e. alicyclic compound exhibiting no alkali-solubility and carboxylic acid compound strongly exhibiting an alkali-solubility. Accordingly, when a resist pattern is formed by using such a resist, it is not avoided that only the portion exhibiting the alkali-solubility dissolves in case of development to cause heterogeneous dissolution. As a result, sufficient resolution is not easily obtained and a crack or a surface roughness is liable to be caused by partial dissolution at the non-exposure part of the resist film so that a reproducibility of the pattern formation was low. Furthermore, a developer penetrates into an interface between a resist film and a substrate. In the worst case, a pattern collapses. In addition, such a copolymer is liable to cause phase separation and dissolution into a solvent is heterogeneous and, therefore, there is a large problem about selection of a solvent for coating and coating properties onto the substrate.
A resist containing a conjugated heteroaromatic ring compound is proposed in Jpn. Pat. Appl. No. 5-4953. Such a resist is superior in dry etch resistance, and the alkali-solubility, solubility in a solvent and adhesion with a substrate are the same as those of a conventional phenol resin. However, since the transparency to the above short-wavelength light is inferior to the former, a pattern can not be formed in high precision.
As described above, it is desired to develop a resist material which exhibits high transparency to short-wavelength light such as ArF excimer laser and F.sub.2 excimer laser with excellent alkali-solubility, and which has good resolution and good reproducibility as well as sufficient dry etch resistance for a fine working. However, a resist material provided with such conditions is still to be obtained.
In order to obtain sufficient dry etch resistance, an alicyclic compound is preferably a polycyclic one and, therefore, a bulky substituent tends to be selected as a substituent of an acrylic ester.
However, when a bulky alicyclic compound is selected as a substituent in order to improve the dry etch resistance, the following disadvantage arises. That is, an acidic group which imparts an alkali-solubility to a polymer, such as carboxyl group, constitutes a backbone chain of the same acrylic unit of a copolymer, together with the alicyclic compound. Therefore, a distance from the backbone chain of the acidic group normally becomes shorter than that of a bulky ester group. In case of a high-dimensional structure of the copolymer, it is not avoided to be exerted by an influence of steric hindrance of an alicyclic substituent having high hydrophobic nature. That is, approach of the alkaline molecular in a developer to an acidic group or an interaction between a resist film and the surface of a substrate is inhibited. Accordingly, it becomes difficult to obtain suitable dissolution characteristics of the resist film to the developer so that sufficient adhesion between the resist film and substrate can not be obtained.
As a result, sufficient resolution cannot be easily obtained and a crack or surface roughness is liable to be caused by partial dissolution at the non-exposure part of the resist film so that the reproducibility of the formation of a pattern was low. Besides, since the adhesion between the resulting resist pattern and substrate is not sufficient, a developer penetrates into an interface between a resist film and a substrate. In the worst case, a pattern collapses.
As a resist which has sufficiently high dry etch resistance and is capable of performing an alkaline development, for example, there is a chemically amplified resist as disclosed in JA-P-63-27829. This chemically amplified resist is a composition containing an alkali-soluble resin, a solubility inhibitor and a compound which is capable of generating an acid by irradiation of an actinic radiation (photo-acid generator), and the solubility in an alkaline developer is inhibited by a solubility inhibitor in the state of non-exposure. On the other hand, when the resist film formed on the substrate is irradiated by ultraviolet rays, X-rays or high-energy electron beam, this photo-acid generator is decomposed to generate an acid. Furthermore, this acid acts as a catalyst by subjecting to a baking treatment, thereby decomposing a solubility inhibitor. Consequently, the light-exposed portion of the resist film selectively exhibit an alkali-solubility and dissolves in a developer to form a pattern. Such a resist is a positive type resist.
Such a chemically amplified resist makes is possible to enhance an alkali-solubility of only the light-exposed portion in the resist film by the following baking step using, as a catalyst, a trace amount of an acid generated by a short-time light exposure, thereby differentiating the solubility from that of the non-exposure portion. Therefore, the formation of a resist pattern using the chemically amplified resist has such an advantage that an amount of the exposure light can be reduced and high sensitivity can be easily performed. On the other hand, it is necessary to perform higher sensitization of a resist due to requirements of high densification and high productivity of a device.
In the chemically amplified resist, high sensitization can be performed by baking at high temperature at the step following the light exposure, thereby allowing to proceed a thermal reaction. However, long-time baking is generally accompanied by deterioration of a pattern profile. A method of adding a large amount of a photo-acid generator as a catalyst of the thermal reaction to increase an amount of an acid generated by the light exposure is also considered to be an effective technique. In this case, however, the transparency in the wavelength of the exposure light is lowered, thereby also causing deterioration of a pattern profile. In an electron beam resist whose transparency is not a particular object, the improvement in sensitivity by such a technique is advantageous. On the other hand, a reduction in drawing time as a result of the realization of high densification of the device is a large problem in view of photolithography so that high sensitization of the resist is desired.
As described above, a measure capable of performing the improvement in sensitivity, which is better than that by the chemically amplified resist, is required as a resist having an alkaline-solubility, high dry etch resistance and high sensitivity. Particularly, in a 1 Gbit DRAM device, the production by an electron beam direct drawing is now studying and high sensitivity is essential. Therefore, a measure of high sensitization having an effect larger than that of the chemically amplified resist has been required.